Highly asymmetric triblock polymer compositions and methods of making same

Abstract

A styrenic triblock copolymer composition with a combination of excellent tensile strength and high melt index, excellent for manufacturing, finishing and handling, forming stable pellets, for use in applications including but not limited to adhesive, coating, and flexographic printing. The composition comprises a first block which is a polymer of a monoalkenyl arene; a second block which is polymer of a conjugated diene and a third block which is a polymer of a monoalkenyl arene wherein a peak molecular weight of the third block is from about 0.06 to about 0.4 times that of the first block.

The invention claimed is: 
     
       1. An adhesive composition comprising:
 from 30 to 60 wt. % of a highly asymmetric triblock (“HAT”) copolymer, 
 from 30% wt. to 60% wt. of a tackifying resin, 
 from 0 to 45 wt. % of an oil, 
 and from 0.1 to 3 wt. % of an anti-oxidant, wherein the wt. % is based on the total weight of the adhesive composition; 
 wherein the HAT copolymer comprises a first block which is a polymer of a monoalkenyl arene, a second block which is a polymer consisting of a conjugated diene, and a third block which is a polymer of a monoalkenyl arene, wherein:
 the block copolymer has a peak molecular weight ranging from 10,000 to 500,000 g/mol, 
 the third block has a peak molecular weight ranging from 0.06 to 0.4 of the peak molecular weight of the first block; and 
 wherein the HAT copolymer has a total arene content ranging from 15 to 40 wt. %. 
 
 
     
     
       2. The adhesive composition of  claim 1 , wherein the HAT polymer comprises mixtures of copolymers having formula A1-B-A2 or (A2-B-A1) n X,
 wherein both A1 and A2 are monoalkenyl arene blocks, 
 B is a conjugated diene block, 
 n is an integer from 2 to 6, 
 X is the residue of a coupling agent, and 
 the A1 block has a peak molecular weight that is at least 2.5 times the peak molecular weight of the A2 block. 
 
     
     
       3. The adhesive composition of  claim 1 , wherein the HAT copolymer has the formula (A2-B-A1) n X, wherein X is the residue of a coupling agent, and wherein the copolymer is bound to the coupling agent at the A2 block. 
     
     
       4. The adhesive composition of  claim 1 , wherein the HAT copolymer is blended with at least a second polymer which is different than the HAT copolymer, forming a blended HAT copolymer. 
     
     
       5. The adhesive composition of  claim 1 , wherein the HAT copolymer is characterized as having a tensile strength of from 0.1 MPa to 10 MPa as determined in accordance with ASTM D412 or ASTM D638. 
     
     
       6. The adhesive composition of  claim 1 , wherein the HAT copolymer is characterized as having a melt index ranging from 5 g/10 min to 200 g/10 min. as determined in accordance with ASTM D1238 measured at 200° C. with a 5 kg mass. 
     
     
       7. The adhesive composition of  claim 1 , wherein the conjugated diene is hydrogenated for a hydrogenated highly asymmetric triblock copolymer. 
     
     
       8. The adhesive composition of  claim 1 , wherein the second block is a mixed midblock with amounts of two dienes in a ratio ranging from 10:90 to 90:10. 
     
     
       9. The adhesive composition of  claim 1 , wherein the second block is a mixed midblock with mixtures of isoprene and butadiene or butadiene and myrcene. 
     
     
       10. The adhesive composition of  claim 1 , wherein the conjugated diene block is formed from a butadiene monomer or an isoprene monomer that is a substantially pure monomer. 
     
     
       11. The adhesive composition of  claim 1 , wherein the second block is a mixed midblock comprising butadiene and isoprene, and wherein the butadiene is present in an amount of at least 20% wt. the total weight of the entire second block. 
     
     
       12. The adhesive composition of  claim 1 , wherein the conjugated diene block is formed from a butadiene monomer, and wherein the conjugated diene block has a vinyl content ranging from 8 mol % to 95 mol %. 
     
     
       13. The adhesive composition of  claim 1 , wherein the conjugated diene block is formed from a butadiene monomer or an isoprene monomer containing up to 10% by weight, of structurally related conjugated dienes selected from 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene and 1,3-hexadiene and 7-methyl-3-methylene-1,6-octadiene. 
     
     
       14. The adhesive composition of  claim 1 , wherein the polymer of a conjugated diene is formed from a butadiene monomer, and wherein the conjugated diene block has a vinyl content that progressively increases across the block. 
     
     
       15. The adhesive composition of  claim 1 , wherein the HAT copolymer is in pellet form. 
     
     
       16. A label or a surface protection film formed by laminating or applying an adhesive layer comprising the adhesive composition of  claim 1 . 
     
     
       17. The adhesive composition of  claim 1 , wherein the tackifying resin is selected from the group consisting of C5 hydrocarbon resins, C5/C9 hydrocarbon resins, hydrogenated and partially hydrogenated C9 hydrocarbon resins, rosin esters, terpenes and styrenated terpene resins.